Visco-elastic foams are usually produced from a polyol blend comprising a rigid polyol having an OH value of 180-400. This provides drawbacks. The first problem is that this rigid polyol is usually all PO, thus with only secondary hydroxy groups, and thus less reactive. The second drawback is that this rigid polyol leads to highly crosslinked foams, thus with lower mechanical properties (i.e. tear strength and elongation are quite low). The third drawback is that the flow quality is poor (due to an early network formation). See e.g. U.S. Pat. No. 4,839,397; U.S. Pat. No. 5,847,014; and WO-A-9816567.
Co-pending application PCT/EP00/09732 aims at solving these problems and at providing easy processable visco-elastic foams without resort to hard polyol by using the below described polyols b1, b2, b3 and b4. The visco-elastic foams obtained in this way show a relatively low relaxation factor. Surprisingly, it has been found that the relaxation factor can be improved by using a monool in such process.
While the use of monools is known in the prior art, nothing in the prior art discloses or suggests how to increase the relaxation factor of visco-elastic foams using such monools. See e.g. EP 913414; WO96/06874; WO01/57104; and EP386974.
The instant invention also aims at providing a flexible polyurethane foam which exhibits a low compression set, a very low resilience (good damping), a good tear strength, a very high elongation, a high loss factor and a soft feel.
The instant invention also aims at providing a system of wide range of processability (wide range of 2, 4′/4, 4′ ratio for MDI), of low viscosity for the ingredient streams (which would be especially useful for making mouldings for sound insulation, and which could be used on state-of-the-art polyurethane machinery).